The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Engine management systems may need to generate an engine-out NOx estimate or measurement for after-treatment control systems. For example only, the after-treatment control systems may use the NOx estimate or measurement for lean NOx trap (LNT) fill estimation, reductant metering strategies in selective catalyst reduction (SCR), etc.
Some engine management systems use a NOx sensor arranged in an exhaust stream to directly measure the NOx level. However, the NOx sensor is expensive and tends to fail over the life of a vehicle, which may increase warranty costs. Other engine management systems generate the NOx estimate using a model instead of directly measuring the NOx level using the NOx sensor. For example only, the model may use a map or table that outputs the NOx estimate based on engine speed, load and/or other variables. While this approach is less expensive, it tends to be less accurate than engine management systems that directly measure the NOx level using the NOx sensor.